Am I missing something? Are there tiles/deals that let players put down extra houses (I know there are ways to put down extra rails)?
There are two deals that allow you to place buildings (one as a station and one as a telegraph office).
Repeatedly using a turquoise worker to build track is about the only way you can potentially speed it up, but not by much.
To add up to what Paul wrote, using only the pieces at the left of the logo and not the ones at the right will also speed the game up.
i.e Lets say you have 2 buildings to the right of your logo and 4 rails remaining (2 to the left and 2 to the right).
If you choose to build rails (or trade) as your next actions, the game will last a round or two shorter than if you built stations and offices.